This invention relates in general to crankshafts and, in particular, to an improved construction for a crankshaft which reduces manufacturing costs and provides greater latitude in manufacturing techniques.
This invention is especially suitable for use in a scroll type compressor wherein a pair of mating scrolls, each of which has an involute spiral wrap of similar shape mounted on respective base plates, undergo mutual rotation so that the scrolls orbit one another. In such compressors one scroll is held fixed and the other is orbited to revolve, but not rotate, by means of an Oldham ring or other anti-rotating structure. A compressible fluid, such as a refrigerant gas, is introduced at the side of the spiral wraps and is compressed as the gas moves under the orbiting motion of the device. The compressed gas is then discharged at the center. By reversing the process, introducing compressed fluid at the center and permitting the fluid expansion to drive the device, a scroll machine can be used as a motor.
Because the orbiting motion of the moving scroll is unbalanced and off axis, a vibrating moment is created which must be appropriately balanced by a suitable counterweight. Current designs for scroll-type compressors, or other scroll-type rotating machines, require that the counterweight be positioned a considerable axial distance away from the orbiting scroll that the counterweight is intended to counterbalance. Such counterweights are carried by the rotor crankshaft, but fabricating a crankshaft which includes a rotor-mounted counterweight by known manufacturing techniques is very expensive. Such existing fabrication processes include machining a single cast piece of iron, gray or ductile, or machining the crankshaft from a forging. Regardless of which of these basic fabrication processes are utilized, the crankshaft must be machined from a single, substantially homogeneous, piece of material thereby requiring substantial manufacturing costs.